How do I add a label search to my pages index?or
How do I add a post to my labels index?or even
How do I add a link to another blog as a page index entry?And right now, you can't do any of these things, to a standard pages index.
A Pages Index gadget indexes the static pages in your blog. Period.
But as I've written before, a pages index is nothing more than a linklist (in the sidebar), or a horizontal menu bar (under the blog header), with the links to the pages enumerated in the linklist or menu bar.
A linklist is easy enough to make - that's just a simple gadget, in "Page Elements". A horizontal menu bar isn't all that much harder to make.
Just find the Pages List for the blog, and for each page, extract the page title, and the page URL. Each page title combined with the page URL becomes one clickable link in the linklist or horizontal index. When you want to add non pages to the pages index, those are simply more entries - a caption / title + a URL becomes yet one more clickable link in the linklist or index.
Then style the linklist or index, as you like.
The one thing that you won't get is a cute gadget, that morphs between a horizontal tab bar and a linklist, as you re position it below the header, or in the sidebar. You have to plan where you want your index, and style it accordingly. Other than that, it's a 30 minute task to make one or the other.
If you like the look of the Static Pages Tabs Index gadget, particularly in a Designer Template - but you want to index labels and / or post pages, you will need to use a linklist in place of the Pages gadget.